Conventionally, papermaker's felts have been formed by weaving a fabric base and then needling fibrous batts to the base. The use of woven fabric has certain disadvantages. The fabric is normally woven in endless configuration on a loom and due to the size of the felt, a very lengthy set-up time is required before the weaving operation can begin. When fabricating felts of substantial size, it may take a group of workmen several days to set up the loom before weaving can commence. Furthermore, since felts are generally becoming larger, the size of the loom required is also becoming larger.
The shuttle, which is used in the conventional weaving operation to interleaf the cross yarns with the warp yarns, is only capable of containing a limited quantity of yarn and after deletion of the yarn, additional lengths of yarn must then be overlapped with the trailing end of the original length, resulting in pressure points in the completed felt.
As a further problem, the normal weaving process produces distortion of the yarns at the side edges of the woven fabric and non-uniformity in spacing between the yarns. The non-uniformity must normally be corrected through tedious manual operations.
A further disadvantage of utilizing a woven fabric in a papermaker's felt is that the points of crossover between the cross yarns and the warp yarns act as pressure points and can cause disfiguration of the paper web. It has also been recognized that cross yarns impede the drainage characteristics of the felt which can adversely affect the felts performance on the papermaking machine.
To overcome the disadvantages of a woven base fabric, attempts have been made in the past to minimize or eliminate the cross yarns (yarns that extend across the machine direction) in the base fabric. One proposal has been to minimize the number of cross yarns and to utilize cross yarns of fine denier. However, felts of this type still must be prepared by the conventional weaving process, and extreme care must be taken to maintain the integrity of the fine cross yarns during handling.
A second proposal, as suggested in the past, has been to use water soluble cross yarns. After the fabric is woven by conventional weaving processes and subsequently needled, the felt is subjected to a water treatment to dissolve the cross yarns.
Another proposed, as set forth in U.S. Pat. No. 3,097,413, is to lay the warp yarns on a watersoluble plastic film, and after needling, the felt is subjected to a water treatment to dissolve the film, with the result that the finished felt contains only longitudinal yarns without cross yarns.